Purpose: There are „sensitive phases“ in the development of an embryo, where certain environmental stress factors have a strong influence on the performance of later epigenetic adaptation mechanisms. In these phases the animal often acquires a predisposition for diseases occurring at an adult age. After the maturation of the embryo"s adrenal cortex, alternating incubation temperatures result in an alternating cortisol concentration. Cortisol regulates the energy flow in the direction of allocation. The glucocorticoids are important among other things for the chicken to slip in time, the surfactant synthesis (maturation of the lung) and the embryonic glucose metabolism. The purpose of this analysis was to investigate if temporarily lowering the temperature to 21 C° can lead to changes in cortisol concentration in the blood or in the allantois liquid and as a result to altered biological effects.
Method: Incubation conditions: Incubator with automatical turnover of eggs and ventilation system, humidity 60%, temperature adjustment as necessary. There have been comparative studies of cortisol concentration in blood plasma and allontois liquid. The control groups consisted of 10 eggs each for the types D14, D16 and D18. The eggs were continuously incubated at 37,5 C°. Shortly before the sample taking the eggs of the same control groups were cooled at 21 °C for 30 minutes. The cortisol level was determined with the help of the enzyme-immuno-test-kit (BOEHRINGER MANNHEIM). The measurement was accomplished with the spectral photometer ULTRSPEC (Pharmacia LKB, Sweden) at a wave length of 420 mm.
Results: A comparable cortisol concentration was found in the allantois liquid and in the plasma of the three control groups (37,5 °C). There is an age-related increase (30,5 to 43,5 ng/ml). The brief lowering of the temperature (to 21°C) had no effect on the cortisol concentration in the plasma. In all age groups though the allantois liquid level is significantly lower (13,9 - 34,3 ng/mm) than in the control groups (36,0 - 49,3 ng/ml). Also in the case of temperature lowering the age-related increase is apparent.
Conclusion: The differing concentration levels in the allantois liquid and in the plasma hint to the assumption of a barrier between both. The allantois liquid serves as a repository which can deliver cortisol, should the embryo cool down. Thus the blood values and the biological effects are kept on a normal level. As a result the embryo will have enough energy when preparing to slip despite the influence of cold temperatures as a stressor. Moreover cortisol enables the continuous lung maturation and thus the transition of allantois to lung breathing.